Trace detection has various important applications, such as, for example, screening of individuals and baggage at transportation centers, facility security, military applications, forensic applications, and cleaning validation.
Modern detection equipment can detect target compounds in the nanograms to picograms range, but effective detection requires obtaining a suitable sample. Various sampling methods are known and mainly involve vapor and particle sampling. For example, U.S. Pat. No. 4,909,090 teaches the use of hand operated vapour samplers which heats the surface to assist in dislodging vapours, which are trapped on collector surfaces in the probe. However, because some target compounds have low vapor pressures, this method can have somewhat limited usefulness.
Particle collection methods are also known. Particle collection techniques include surface inspection by means of physical particle collection in minute amounts, the use of dust pan-brush arrangements, vacuum suction onto porous or semi-porous substrates, filters, membranes and the like, and the use of swabs, swipes, gloves, etc. U.S. Pat. Nos. 3,970,428, 4,220,414, 4,192,176, and 5,425,263 are directed to particle collection methods useful for forensics and surface geochemical exploration where trace metals and organometals can be useful as pathfinder indicators in mineral exploration activities. U.S. Pat. No. 5,476,794 describes collection of sample particles with a glove and the use of an intermediate step involving vacuum suction off the glove.
Another method for collecting trace particles involves insertion of a filter disk into a suction line of a vacuum cleaner unit to remove particles for analysis by suction. After a sufficient quantity of dust/material is collected, the filter disk or substrate is removed and presented to an analytical device. The filter disk is inserted into a thermal desorption device which is rapidly heated to volatilize the collected material. The heating process converts the trace particles to vapors for conventional chemical vapor analysis, such as, for example, IMS, mass spectrometer or gas chromatography or such other instrument. This method suffers from the disadvantage of vacuum cleaner contamination and requires manipulating a cumbersome vacuum cleaner to obtain a sample.
Collection media in the form of hand coverings, such as gloves, mitts and swipes have been used in various forms for particle collection, but these techniques often require an intermediate step that transfers the sample collected on the a glove or the like to the analytical device. One method involves exposure of the collection medium to a suction device to vacuum the glove or mitt, as described in U.S. Pat. No. 5,476,794. This method is time consuming and the vacuum transfer is inefficient, causing a loss of sample due to incomplete transfer from the collection medium. Additionally, vacuum suction devices are noisy, cumbersome, and require power to energize the suction motors. Even small vacuum sampling devices have relatively limited battery lives. Moreover, the suction device can be contaminated during transfer of a sample containing a target compound requiring thorough cleaning before the next use. Finally, often an even greater problem is created by the suction causing collection medium fibers and lint to be released which can either obstruct the analytical device, present interfering chemicals or fluff/lint which might compete in the analytical process, as for example, if ion mobility spectrometer (IMS) is used where matrix effects from the hand covering material can compete too aggressively in the ionization process.
U.S. Pat. No. 5,476,794 describes collection of particles where the particles are transferred from a sample collection glove to a collection probe, and the complete probe is inserted into the analyzer to vaporize the samples. This technique involves a complex sampling probe, which can be easily clogged by debris and lint from the sampling gloves.
Conventional sampling substrates, which are handheld and cover the fingers are also known for collecting particles from surfaces, where the material is inserted directly into the analytical device. These materials have the advantage of avoiding an intermediate transfer step and the use of a suction device. However, collecting samples by hand can result in contamination or incomplete collection of a sample due to insufficient pressure of the sampling substrate against the item being analyzed.
Moreover, conventional sampling substrates often rely on the operator to ensure that the sampling area of the substrate material (or “swab”) is properly aligned within an analyzer (or “analytical device”), so that the portion of the substrate material containing the sample is actually analyzed by the analytical device. For example, in IMS it is necessary that the collected sample is properly aligned on the sample desorber such that the collected sample is desorbed and analyzed by the IMS. When the sample area of the substrate is not properly aligned within the analyzer, the collected sample cannot be completely desorbed. Therefore, the test results of the sample can be affected by how the sample area of the substrate is aligned within the analyzer.